1. Field of the Invention
The present invention relates to a coating material for an electric wire, and more particularly to a polyester resin composite, in which flexibility is not lost by a thermal hysteresis and the flame-resistance is superior. The resin composite is obtained by adding bislactam compounds to halogen-containing flame-resisting aromatic polyester copolymers. The present invention is also concerned with an electric wire coated the resin composite.
2. Prior Art
Rubber, polyvinylchloride, polyethylene, polypropylene, nylon and the like have been used as a coating material of an electric wire. In particular, an important position has been given to polyvinylchloride in view of its flame-resistance and mechanical strength. Recently, as a result of where these coating materials are used, requirements of the coating materials, such as superior heat resistance, electrical characteristics, flame resistance and thin-wall workability for achieving space-saving have become severe and accordingly up-graded.
Fluorine resins, cross linked polyethylene and the like meet these requirements but these materials are inferior in thin-wall workability and also the fluorine resins are expensive, so that it cannot be said that they are satisfactory.
Polyethylene terephthalate and polybutylene terephthalate are gathering interest in view of their superior thin-wall workability, mechanical strength (such as flexibility and abrasion-resistance), heat-resistance and electrical characteristics but they are insufficient in flame-resistance and crystallinity, so that not only is their flexibility remarkably lowered by the thermal hysteresis, such as a heat treatment after coating and heating condition during use, but also the mechanical strength, such as impact resistance, are lowered. Accordingly, use near a heat source must be avoided as well as an environment having the possibility where heat may be accumulated. That is to say, their use is materially limited.
In order to overcome these defects, elastomers and amorphous polymers have been added to lower the crystallinity. In addition, in order to maintain the stability of mechanical strength, a partial cross-linkage and the like have been tried.
In the former, a slight improvement in effect is observed but since a crystalline resin matrix exists as it is, polyalkylene terephthalates can not withstand long-range thermal hysteresis. In addition, a defect occurs in that a reduction in the share of crystalline resin leads to a deterioration of mechanical characteristics such as frictional abrasion.
In addition, in the latter case, a slight improvement in the stability of the mechanical characteristics resulting from the cross-linkage is observed but defects occur in that the flexibility is sacrificed and the progress of the cross-linking reaction leads to a complicated control, so that the workability is remarkably lowered.